This invention relates to an electric arc furnace which comprises a shell portion having many water-cooling boxes, instead of refractory bricks, along its inner circumferential surface and a furnace bed portion which is made slightly larger in diameter than the shell portion. The two portions are made separately and the shell portion is laid upon the bed portion to be combined into a furnace proper.
In a conventional electric arc furnace for use in steel making, the furnace wall is constructed by stacking refractory bricks as shown in FIG. 8 of the accompanying drawings. Since the refractory bricks in the vicinity of the three electrodes usually disposed in the furnace, i.e. the refractory bricks at the so-called hot spot, are subjected to the high heat of electric arcs and may reach a temperature of about 3,000.degree. C., high class refractory bricks are used at the hot spot. Due to a recent trend towards operating such a furnace at higher power, using a transformer of large capacity for obtaining the high productivity, the refractory bricks which constitute the furnace wall are subjected to a higher heat and as a result, the service life of the furnace wall has been considerably shortened. The refractory bricks at the hot spot which are subjected to an exceedingly high heat soon yield to the high heat, in some cases only several days after the furnace wall was last repaired. As a countermeasure to such disadvantage, the present practice is to carry out repairs while the refractory bricks are still hot, i.e. before scrap is charged after each teeming, refractory is sprayed upon the surface of the refractory bricks, thereby reinforcing the refractory bricks of the furnace wall. However, this method has the drawback of requiring much labour for reinforcing of the refractory bricks after each teeming, thus lowering productivity and increasing the cost of steel manufacturing.
Furthermore, in the case of a conventional furnace with a shell portion and a bed portion made as single unit, the refractory material of the shell portion and those of the bed portion differ in useful lives, that is, the useful life of the former is shorter than that of the latter. This difference in useful lives is attributed to the influence of arcs, temperature, scrap and other factors in the furnace. Thus, whenever any damage is sustained by refractories of the shell portion, even if the refractories of the bed portion are still in good condition and need no repair, the use of the furnace must be suspended while the damaged refractories of the shell portion are repaired, with the result of a lowering of the operating efficiency of the furnace.